Jenson Button's decision to leave BAR for Williams in 2005 is "crazy", according to rival Juan Pablo Montoya.

The Colombian, who is leaving Williams for McLaren in 2005, said he "did not understand" Button's decision.

"Maybe there's something in BAR he doesn't like or something," he said. "The whole team was built around him.

"I think it's crazy, but it's his choice. Probably Williams can turn it around, but they got it completely wrong this year."

BAR are fighting Button's decision to sign for Williams, claiming they have a valid
contract for him to drive for them in 2005.

It will be interesting to see what happens between Jenson and Mark Webber

Juan Pablo Montoya

Button's management team insist that BAR failed correctly to take up their option on the Englishman and that he is legally allowed to switch teams.

Montoya declared BAR are the more competitive team, even if Button believes Williams will give him a better chance of winning the world championship next year.

Montoya added: "BAR's results were getting better. In the last race, he had a 10-place penalty and finished second.

"After that, how your mind goes to go somewhere else I don't know.

Montoya has become frustrated at Williams

"Williams have to come a long way. They proved last year it can be done and this year will maybe help them do so because they got it completely wrong."

Montoya, whose Williams team have abandoned the walrus-style nose of their car for
this weekend's race in an attempt to improve its performance, also implied that Button
might have problems dealing with the highly-rated Mark Webber as his team-mate next year.

"It will be interesting to see what happens between Jenson and Mark in the team,
Webber being Australian and [technical director] Sam Michael being Australian, you
know."